Gate valves are often used in applications where the fluid mediums are very destructive of the internal parts of the valve; namely, the seats, gate, seals and the internal surfaces of the valve body. This is particularly true of valves used in the chemical, petroleum, and marine industries. The abrasive and corrosive nature of these applications, and especially at elevated temperatures and pressure, places greater emphasis on the proper selection of materials for the valve body, and the internal parts.
Heretofore it has been necessary, in some applications, to line the internal surfaces of the valve to resist the corrosive action of the medium. Because of the excessive wear in the above applications, it becomes necessary to remove and replace the seats, gate and stem frequently. Most valve bodies are cast iron and are very susceptible to corrosion, making the valve seats difficult to remove and replace. The valve refurbishment requires that new seats be threaded or welded in place in the body, and then remachined to match a new replaced wedge type gate. This is an expensive and time-consuming operation. In order to install or remove the valve seats or gate the interior of the valve must be accessed through the valve bonnet. As a result, the bonnet flange becomes very massive, since at high pressures and temperatures the bonnet and valve cavity must be designed as a high pressure vessel. This results in heavy wall thicknesses, heavy bonnet flanges, and bolts. This is especially true of the larger valves. The resulting massiveness of the larger valve makes it very expensive and impractical to make the entire body from suitable materials such as stainless steel and other metal alloys.
The objective of this invention is to overcome the above stated difficulties by making the body from a single piece of material and considerably lighter. In addition, the internal parts are all removable from the flowpath of the valve, and easily replaced by unbolting and removing the body portion of the valve from the pipeline. The valve body does not have a bonnet or access cover of any type, but takes the form of a unitized piece of material of high strength, corrosion resistant, and of low porosity.